Membranes provided within a separation facility can be treated using clean-in-place (CIP) methods to provide flushing, rinsing, pretreatment, cleaning, sanitizing and preserving, as filtration membranes have a tendency to foul during processing. Fouling manifests itself as a decline in flux with time of operation. Flux decline is typically a reduction in permeation flow or permeation rates that occurs when all operating parameters, such as pressure, feed flow rate, temperature, and feed concentration are kept constant. In general, membrane fouling is a complicated process and is believed to occur due to a number of factors including electrostatic attraction, hydrophobic and hydrophilic interactions, the deposition and accumulation of feed components, e.g., suspended particulates, impermeable dissolved solutes, and even normally permeable solutes, on the membrane surface and/or within the pores of the membrane. It is expected that almost all feed components will foul membranes to a certain extent. See Munir Cheryan, Ultrafiltration and Microfiltration Handbook, Technical Publication, Lancaster, Pa., 1998 (Pages 237-288). Fouling components and deposits can include inorganic salts, particulates, microbials and organics.
Filtration membranes typically require periodic cleaning to allow for successful industrial application within separation facilities such as those found in the food, dairy, and beverage industries. The filtration membranes can be cleaned by removing foreign material from the surface and body of the membrane and associated equipment. The cleaning procedure for filtration membranes can involve a clean-in-place CIP process where cleaning agents are circulated over the membrane to wet, penetrate, dissolve and/or rinse away foreign materials from the membrane. Various parameters that can be manipulated for cleaning typically include time, temperature, mechanical energy, chemical composition, chemical concentration, soil type, water type, hydraulic design, and membrane materials of construction.
Chemical energy in the form of detergents and cleaners can be used to solubilize or disperse the foulant or soil. Thermal energy in the form of heat can be used to help the action of the chemical cleaners. In general, the greater the temperature of the cleaning the solution, the more effective it is as a cleaning treatment, although most membrane materials have temperature limitations due to the material of construction. Many membranes additionally have chemical limitations. Mechanical energy in the form of high velocity flow also contributes to the successful cleaning of membrane systems. See Munir Cheryan, Ultrafiltration and Microfiltration Handbook, Technical Publication, Lancaster, Pa., 1998, pages 237-288.
In general, the frequency of cleaning and type of chemical treatment performed on the membrane has been found to affect the operating life of a membrane. It is believed that the operating life of a membrane can be decreased as a result of chemical degradation of the membrane over time. Various membranes are provided having temperature, pH, and chemical restrictions to minimize degradation of the membrane material. For example, many polyamide reverse osmosis membranes have chlorine restrictions because chlorine can have a tendency to oxidatively attack and damage the membrane. Cleaning and sanitizing filtration membranes is desirable in order to comply with laws and regulations that may require cleaning in certain applications (e.g., the food and biotechnology industries), reduce microorganisms to prevent contamination of the product streams, and optimize the process by restoring flux. See Munir Cheryan, Ultrafiltration and Microfiltration Handbook, Technical Publication, Lancaster, Pa., 1998, pages 237-288.
Other exemplary techniques for cleaning filtration membranes are disclosed by U.S. Pat. No. 4,740,308 to Fremont et al.; U.S. Pat. No. 6,387,189 to Groschl et al.; U.S. Pat. No. 6,071,356 to Olsen; and Munir Cheryan, Ultrafiltration and Microfiltration Handbook, Technical Publication, Lancaster, Pa., 1998 (Pages 237-239).
It is believed that membrane performance declines dining processing of milk, whey, and other feed streams due to the fouling of the membrane surface or membrane pores by protein, fat, minerals, and other feed stream components.
The fouling of membranes processing high solid feed streams therefore require that they are cleaned regularly using a clean-in-place (CIP) approach in which the use of alkaline, acid, and cleaning adjuvants such as surfactants and water conditioning polymers aid in the cleaning of the foulants and restore the membrane for functional use.
The proper use of alkaline, acid, and adjuvants requires an understanding of the functionality of the chemistry used. As an example, too high in pH or too low in pH can damage the polymeric membrane material. The use of solvents or overuse of surfactants can often time lead to destruction of the glue line causing the membrane to delaminate rendering it non-functional. Overusing oxidative chemicals such as sodium hypochlorite (chlorine bleach) or hydrogen peroxide can Irreversibly damage some polymeric membrane types.
Conventional cleaning compositions used in CIP protocols, particularly those intended for institutional use, often contain alkyl phenol ethoxylates (APEs). APEs are used in cleaning compositions as a cleanser and a degreaser for their effectiveness at removing a variety of soils from a variety of surfaces. Commonly used APEs include nonyl phenol ethoxylates (NPE) surfactants such as NPE 9.5 or nonoxynol-9 which is a 9.5 mole ethoxylate of nonyl phenol.
However, while effective, APEs are disfavored due to environmental concerns. For example, NPEs are formed through the combination of ethylene oxide with nonylphenol (NP). Both NP and NPEs exhibit estrogen-like properties and may contaminate water, vegetation and marine life. NPE is also not readily biodegradable and remains in the environment or food chain for indefinite time periods. There is therefore a need in the art for an environmentally friendly and biodegradable alternative that can replace APEs in membrane cleaners which allow membranes to be adequately cleaned from soils, do not cause damage to the membranes or membrane construction materials, and do not foul the membranes themselves.